Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $244.53   8.320%   $264.8749   $264.87   $264.85   $264.90  
  Purchase #2 $237.82   10.566%   $262.9481   $262.95   $262.95   $262.90  
  Purchase #3 $46.64   7.619%   $50.1935   $50.19   $50.20   $50.20  
  Purchase #4 $210.33   4.158%   $219.0755   $219.08   $219.10   $219.10  
  Purchase #5 $226.92   4.111%   $236.2487   $236.25   $236.25   $236.20  
  Purchase #6 $35.70   3.129%   $36.8171   $36.82   $36.80   $36.80  
  Purchase #7 $32.34   3.469%   $33.4619   $33.46   $33.45   $33.50  
  7 purchase totals = $1,034.28       $1,103.6197   $1,103.62   $1,103.60   $1,103.60